The present invention relates to an apparatus for measuring fluid flow rate in a two-phase flow stream and, more particularly, to a pitot tube type flow rate measuring apparatus uniquely designed to measure flow rate in a flow of a gas containing liquid droplets.
In installations such as the spray towers of wet gas scrubbers, the gas flow in and downstream of the spray tower is heavily laden with liquid droplets entrained in the gas flow. It is often desirable to measure the flow rate of this two-phase fluid through the spray tower and gas flow passages downstream thereof. In order to do so, a flow meter must be utilized which can operate in this wet gas environment without interference from the liquid droplets in the gas.
The most typical prior art pitot tube type flow meters comprise a concentric tube device wherein the interior tube is open at its end and orientated so that the end opening faces directly into the gas flow stream to measure total pressure, while a series of smaller openings, i.e. holes, are drilled about the circumference of the outer tube at a location downstream of the total pressure opening to the inner tube. The smaller openings measure static pressure and are open to the annular space between the inner and outer tubes. Although such a pitot tube design is completely satisfactory for use in a dry gas flow, the smaller static pressure holes tend to become blinded, i.e. clogged, by water droplets when such a pitot tube design is utilized in a wet gas environment. Accordingly, such pitot tubes has proven unsatisfactory for use in measuring flow rate in and downstream of the spray towers in gas scrubbers.
Another type of prior art pitot tube utilized for measuring gas flow rates is commonly referred to as the stauscheibe pitot tube. This type of pitot tube typically consists of two laterally adjacent tubes, one of which has a opening facing directly upstream into the gas flow to sense total pressure while the other tube has an opening facing directly downstream with respect to gas flow to sense the static pressure. A problem associated with using this type of tube in a wet environment such as that of a spray tower is that the gas flow through a spray tower is generally vertically upward. As a result, liquid droplets tend to deposit under the influence of gravity on the downstream static pressure opening which, in the case of a vertical upward flow, as typical in the spray tower, is facing upward.
Accordingly, it is the principle object of the present invention to provide a pitot tube type apparatus for measuring flow rate in a wet gas stream wherein the potential for blinding of the static pressure opening of the apparatus is minimized.